The invention relates to a rack-and-pinion gear, in particular for a rack-and-pinion steering of a motor vehicle.
In conventional rack-and-pinion steering assemblies, a rack is coupled to vehicle wheels for use in controlling the direction of the wheels, a pinion arranged on an input shaft meshes directly with the rack. The pinion radius is relatively small, the axes of the rack and of the input shaft are therefore at a slight distance from one another, the order of magnitude of which is predetermined by the radius of the pinion.
DE 36 27 088 A1 relates to a rack-and-pinion steering assembly, in which the pinion meshing with the rack is designed as a ring wheel with an external and an internal toothing, the external toothing cooperating with the rack and the internal toothing cooperating with a further pinion arranged on an input shaft. In this case, the input shaft is arranged within a sector of the ring wheel, the said sector being in engagement with the rack via the external toothing. There is therefore only a slight distance between the axes of the rack and input shaft.
DE 33 27 979 C1 relates to a rack-and-pinion steering assembly in which a gear with a variable transmission ratio is arranged between a pinion meshing with the rack and a further pinion arranged on the input shaft, the gear is designed in such a way that the axis of the input shaft is positioned at a comparatively slight distance from the axis of the rack.
Rack-and-pinion steering assemblies may present installation problems, at least with respect to present-day vehicles having an engine arranged in the region of the front axle thus limiting space for the rack and pinion and for other components. As a result, installation of both the rack and steering column can be difficult.
The object of the invention is, therefore, to provide new concepts for rack-and-pinion gears and to improve installation of rack-and-pinion steering assemblies.
According to one aspect of the invention, the input-shaft axis and rack axis are separated by a distance which is perpendicular to both axes, the dimension of which is greater than the diameter of the pinion meshing with the rack.
According to this aspect of the invention, the invention provides for interposing gear elements between the input shaft and the pinion meshing with the rack such that the distance between the input-shaft axis and rack axis is increased. According to another aspect of the invention, the input-shaft axis is shifted, relative to a conventional position by use of the interposed gear elements, onto the other side of the rack.
According to one aspect of the invention, there is provision for an interposing pinion meshing with the rack on one side and meshing on its circumferential region located diametrically opposite the region of engagement of the rack, with an input pinion which is arranged on the input shaft, so that the order of magnitude of the distance between the rack axis and input-shaft axis is predetermined by the radius of the input pinion and by the diameter of the pinion meshing with the rack.
This type of construction makes it possible to ensure a particularly efficient design, and it is particularly advantageous that freedom from play can be ensured in the most efficient way, in that the rack is pressed resiliently against the pinion meshing with it and this pinion is mounted so as to be moveable in the pressing direction, so that the pressing forces are transmitted to the radially fixably mounted input pinion of the input shaft. The engagements of the rack and pinion and of the pinion and input pinion are thereby made more efficient and kept free of play in an efficient manner.
According to another aspect of the invention, the rack meshes directly with an input pinion having a large diameter relative to conventional rack and pinion assemblies and provides for a more efficient design and input pinion free of play.